Abstract: Objective：To study the apoptosis of U937 cells induced with lipopolysaccharide (LPS) and interferon-alpha (IFN-a) synergies and its clinical mechanism . Methods：The U937 cells were given with various concentrations of 200ng/ml of LPS and (or) 2000U/ml of IFN-a, the inhibitory ratio was measured by MTT assay, apoptosis rate was detected by flow cytometry ( FCM ) , and the expression of caspase-8 mRNA was measured by reverse transcription-polymerase chain reaction(RT-PCR) after48 hours . Results： LPS in combination with IFN-a could inhibit U937 cell proliferation and increase apoptosis rate in comparison with LPS or IFN-a group (P<0.01), and each drug group are statistically significant compared with the control group(P<0.01)。The expression level of caspase-8 mRNA increased significantly 48h after LPS and IFN-a used in comparison with LPS/IFN-a group and the control group(P<0.01)。Conclusion： LPS in combination with IFN-a can inhibit the proliferation and induce apoptosis of U937 leukemia cells,and the apoptosis mechanism may be related with the activation of caspase-8.

Key words: leukemia, toll-like receptors, U937 cells, interferon-alpha